1. Field of the Invention
The present invention relates to a method of operating a vacuum deposition apparatus in which in a vacuum chamber, an evaporation material is evaporated by heating with a heating device to deposit the evaporation material and form a film on a surface of a long strip base material continuously run by a base material transport device, and also relates to a vacuum deposition apparatus.
2. Description of the Background Art
There has been conventionally used a vacuum deposition apparatus in which in a vacuum chamber, an evaporation material is evaporated by heating with a heating device to deposit the evaporation material and form a film on a surface of a base material. Also, there has been developed a vacuum deposition apparatus for forming a film on a long strip base material, in which in a vacuum chamber, the long strip base material is continuously run by a base material transport device during film deposition. In order to deposit a film on a long strip base material, it is desirable for a deposition apparatus to deposit a film with a uniform thickness in the longitudinal direction of the long strip base material. Therefore, when a film is formed with a uniform thickness in the longitudinal direction of a long strip base material, the amount of deposition is controlled under monitoring of the deposition rate and film thickness. In order to control the amount of deposition, the deposition rate is controlled by adjusting the evaporation rate of an evaporation material with a heating device. The deposition rate may be controlled by adjusting the evaporation conditions such as the degree of vacuum in a vacuum chamber, the transport speed of the base material, and the like.
Methods for monitoring the deposition rate and the film thickness include a method using a crystal oscillator thickness gauge for detecting an amount of deposition from a change in oscillation frequency change of a crystal oscillator or an optical thickness gauge for determining a film thickness by measuring a light transmittance of a base material after the deposition, and a method of theoretically determining a deposition rate by measuring an evaporation rate of an evaporation material using an evaporation rate meter (electron impact type, atomic absorption type, or the like).
Techniques for depositing a film with a uniform thickness on a long strip base material in the longitudinal direction thereof are disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 6-306586 and 8-225940. Japanese Unexamined Patent Application Publication No. 6-306586 discloses a method of depositing a film with a uniform thickness using an ion plating process. In this method, the amount of deposition is controlled by monitoring the amount of evaporation of an evaporation material by measuring a current flowing through a bias electrode generally disposed in an ion plating deposition apparatus or a current flowing through a Faraday cup disposed in the apparatus. Japanese Unexamined Patent Application Publication No. 8-225940 discloses a vacuum deposition apparatus including an optical thickness gauge provided at a measurement point between the start point and the end point of an evaporation zone. The thickness gauge is adapted for measuring the thickness of a film deposited up to the measurement point to determine the thickness of a film finally deposited on a continuous film-shaped substrate and make the thickness uniform by controlling the amount of deposition.
In addition, as another relevant technique, Japanese Unexamined Patent Application Publication No. 2003-13207 discloses a method of depositing a light-absorbing film having a structure composed of dendritically grown metal crystals, in which a film is deposited at a proper deposition rate without monitoring of the deposition rate and thickness. In this method, the elapsed time from the start of a deposition work and the electric power input to an evaporation boat at the elapsed time are previously measured by an experiment of realizing a high-quality light-absorbing film, and the resulting relation between the elapsed time and electric power input is previously stored in a storage device. In subsequent deposition of a light-absorbing film, the electric power supplied to the evaporation boat is controlled to coincide with the power input at the elapsed time stored in the storage device.
However, any one of the aforementioned techniques has the disadvantage below in depositing a film on a long strip base material under monitoring of the deposition rate and film thickness.
When the deposition rate is monitored with the above-described crystal oscillator thickness gauge, a crystal oscillator sensor is disposed near a base material on which a film is deposited so that a film is deposited on the surface of the crystal oscillator to detect an amount of deposition. However, when the thickness (film weight) of the film deposited on the crystal oscillator is increased to some extent, the crystal oscillator does not oscillate or the deposited film is separated from the crystal oscillator. As a result, a change in oscillation frequency of the crystal oscillator cannot be precisely measured. Therefore, in the case of a high deposition rate, the deposition rate can be monitored for only a short time. For example, in deposition at a deposition rate of 50 μm/sec, the deposition rate can be monitored for only about 5 minutes. In another method, a shutter is provided on a crystal oscillator to intermittently monitor a deposition rate, or the deposition rate is monitored by switching a plurality of crystal oscillators. However, in the case of long-term deposition at a high deposition rate, the former method requires a long interval of monitoring of the deposition rate, thereby failing to precisely control the amount of deposition. The latter method has (1) the problem of requiring a large number of crystal oscillators and (2) the problem of scaling-up an apparatus for holding such a large number of crystal oscillators. Therefore, in order to deposit a film on a long strip base material, monitoring is preferably performed for a long time, and thus the crystal oscillator thickness gauge is not practical.
The method using an optical thickness gauge cannot be used for a base material not having light absorption (for example, a metal such as copper).
In use of an electron impact- or atomic absorption-type evaporation rate meter, generally, a window is provided in a deposition apparatus, and light transmitted through the window is detected by a light receiving part disposed outside the deposition apparatus to measure the evaporation rate of an evaporation material on the basis of the light. In this constitution, the evaporation material does not adhere to the light-receiving part, but the evaporation material adheres to the window because the window is provided at a position facing an evaporation source in the deposition apparatus. Therefore, when the deposition time is increased, the window becomes cloudy due to the adhesion of the evaporation material, thereby causing difficulty in precise measurement.
The method disclosed in Japanese Unexamined Patent Application Publication No. 6-306586 requires evaporation and ionization of an evaporation material. However, with some evaporation materials, not all evaporated particles are ionized, or the ratio of ionization varies. Therefore, there may be no correlation between the evaporation amount of an evaporation material and the current flowing through a bias electrode. Also, this method cannot be used for vacuum deposition not requiring ionization of evaporated particles. For the same reason, the method of measuring a current flowing through a Faraday cup cannot be used.
The vacuum deposition apparatus disclosed in Japanese Unexamined Patent Application Publication No. 8-225940 uses an optical thickness gauge and thus cannot be used for the case in which a base material has no light transmissivity or a base material loses light transmissivity due to film deposition.
The method disclosed in Japanese Unexamined Patent Application Publication No. 2003-13207 is used for deposition at a proper deposition rate in forming a good light-absorbing film having a structure composed of dendritically grown metal crystals. The light-absorbing film is formed on a flake-like substrate disposed on a substrate holder in a deposition apparatus.
Therefore, the method disclosed in Japanese Unexamined Patent Application Publication No. 2003-13207 is completely different from a technique for depositing a film with a uniform thickness on a long strip base material in the longitudinal direction thereof.